Foundry mixing machine

ABSTRACT

A foundry mixing machine for preparing a mixture of sand and an admixture is disclosed; the machine has an inlet for the sand, followed by an annular slot for the sand, then an annular admixing space and an outlet for the mixture; a feeding device for the admixture is disposed on the admixing space and leads into the admixing space; between the admixing space and the outlet for the mixture there are disposed two relative to one another rotatable bodies of revolution between which an annular intermediate space is left open for the mixture; the bodies have projections towards the intermediate space; the form of the projections is shown; furthermore improvements on the feeding device for the admixture are shown.

United States Patent 11 1 1111 3,929,320

Haller Dec. 30, 1975 FOUNDRY MIXING MACHINE 3,163,402 12/1964 Yamashita 259/8 3,400,914 9/1968 Benassi 259/8 1751 Invent 3321 2 223 Schheren, 3,503,846 3 1970 Nardi 259/8 [73] Assignee: Escher Wyss Limited, Zurich, FOREIGN PATENTS OR APPLICATIONS Switzerland 249,353 4/1970 U.S.S.R 259/8 Filed! y 1974 Primary ExaminerRobert W. Jenkins [21] AppL NO; 467,143 Attorney, Agent, or Firm-Robert A. Ostmann [30] Foreign Application Priority Data 7 [57] ABSTRACT y 7 1973 Switzerland 6411 A foundry mixing machine for preparing a mixture of Dec 1973 Switzerland "mom/73 sand and an admixture is disclosed; the machine has Dec 1973 Switzerland"" 18O03/73 an inlet for the sand, followed by an annular slot for 1973 Switzerland 3004/73 the sand, then an annular admixing space and an outp 9 1974 Switzerland 4984/74 let for the mixture; a feeding device for the admixture is disposed on the admixing space and leads into the 52 us. or. 259/165- 259/178 A- 259/8 admixing Space; between admixing Space and the 511 int. c1. B28 C 5/16 for the mixture there are disposed relative [58] Field of Search 259/7, 8, 178 A 164, 165 1 to one another rotatable bodies of revolution between 259/168, 161 23, 24, 43 44 66 which an annular intermediate space is leftopen for the mixture; the bodies have projections towards the intermediate space; the form of the projections is [56] References Cited h f th r t th feeding de s own; ur ermore imp ovemen s on e UNITED STATES PATENTS vice for the admixture are shown. 2,313,760 3/1943 McLean 259/8 2,435,884 2/1948 Galewski 259/8 27 Clam, 5 Drawmg Flgures US. Patent Dec. 30, 1975 Sheet 1 of 5 3,929,320

U.S. Patent Dec. 30, 1975 Sheet 2 of5 3,929,320

Elsi

Sheet 3 of 5 US. Patent Dec. 30, 1975 US. Patent Dec. 30, 1975 Sheet 4 of5 3,929,320

Elsi

Sheet 5 of 5 3,929,320

US. Patent Dec. 30, 1975 FOUNDRY MIXING MACHINE BACKGROUND OF THE INVENTION The invention relates to a foundry mixing machine for preparing a mixture of sand and an admixture, said machine having an inlet for the sand, followed by an annular slot for the sand, followed again by an annular admixing space and furthermore, disposed on said annular admixing space, a feeding device for the admixture, leading into the admixing space, and an outlet for the mixture.

A moulding sand mixture, which is prepared in a mixing machine of this kind for example from a sand and a liquid, organic admixture having at least two components, viz a binder and a hardener, is used in foundries for making precision moulds.

The foundry mixing machines which were previously known are relatively big, stationary units from which the mixture has to be conveyed specially to the place where it will be used in the moulding bay of the foundry. Another known foundry mixing machine (U.S. Pat. No. 3,773,299) has the disadvantage that the feeding device has a centrifuge and because of the high speed of the centrifuge there is-a risk of spontaneous combustion of the liquid, organic admixture and possibly its explosion. Furthermore, the known mixing units require several operators. The previous mixing machines also become clogged up in the course of time owing to adhesion of the sticky moulding sand mixture.

SUMMARY OF THE INVENTION The problem underlying the invention is to obviate the above-described disadvantages and to provide a foundry mixing machine which is smaller than the conventional ones, free from trouble and can be used without risk with only a few operators in the moulding bay of a foundry.

This problem is solved according to the invention, on a foundry mixing machine of the type mentioned initially, through the fact that there are disposed between the admixing space and the outlet two bodies of revolution which are rotatable relative to one another, between which a ring-shaped intermediate space is left open for the mixture, and that in this intermediate space on the walls of the bodies of revolution there is a projection towards the intermediate space provided in each case, the projection of one body of revolution and that of the other overlapping one another in the direction perpendicular to the walls of the bodies of revolution.

It is advantageous to the construction of the intermediate space if the projections are solid annular walls and, furthermore, if the projections have, on the mixture inflow side, a surface ascending from the wall of the body of rotation in the direction of throughflow of the mixture. I A complete and safe thorough mixing of the admixture is obtained by the provision of a compressed air line which'conducts the compressed air into the vicinity of the opening of a pipe for the admixture which is provided in the feeding device, preferably by means of the fact that the feeding device opens out into the middle of the annular admixing space and also that the compressed air line opens outside the point at which the admixture pipe opens out.

ble. 0

To allow for a breakdown in operations owing to clogging of the intermediate space lying between the bodies of revolution it is advantageous if at least one of the two bodies of revolution which can rotate relative to one another is held by means of magnetic force to the element supporting it and furthermore that the foundry mixing machine is capable of being divided up so that at least one body of revolution is easily accessi- The foundry mixing machine can be operated by one person only, if a separate stock bin is provided for the sand and for the admixture and a supply line is provided which can be put under pressure, the supply line being fitted with a pilot valve in each case, and if a switching device is provided for switching on the driving motor for the body of revolution and, when the operating speed of the driving motor and the pressure in the supply line has been reached, for opening the pilot valves and also for closing the pilot valves and then switching off the driving motor. Simplification of operation is achieved, moreover, by means of an arm which is mounted so as to swivel relative to the housing of the foundry mixing machine and which in turn is mounted so as to be rotatable about its axis in an upright.

BRIEF DESCRIPTION OF THE DRAWING The subject of the invention is further described and explained with reference to the accompanying drawings, in which:

FIG. 1 is an axial sectional view of one embodiment of the mixing machine.

FIG. 2 is an axial sectional view of a second version of the machine.

FIG. 3 is a partially sectional elevation view of a third version of the machine which employs a casing having three separable sections.

FIG. 4 is a diagrammatic representation of another embodiment of the machine which incorporates various control features.

FIG. 5 is a partly sectioned elevation view of a further version of the machine.

DESCRIPTION OF THE PREFERRED EMBODIMENTS.

In all the figures the same parts of a foundry mixing machine according to the invention have been given the same references.

The foundry mixing machine has an inlet 1 for the sand. Following the inlet 1 is an annular slot 2 through which the sand is conducted into an annular admixing space 3. Disposed on the admixing space 3 is a feeding device which has pipes 5, 6, 60 for the admixture material. The admixture consists of a binder and a hardener which are each led separately into the admixing space 3 through a pipe 5 and 6, respectively, forming part of the feeding device. The pipes 5 and 6 are each provided with a valve 5 and 6 respectively for regulating the supply of admixture. The two components of the admixture are added to and mixed with the sand in the admixing space 3. The mixture of sand and admixture leaves the moulding sand mixer through an oulet 7. In this arrangement the longitudinal axis of the foundry mixing machine is vertical.

Disposed between the admixing space 3 and the outlet 7, for more thorough mixing of the mixture which is mixed together in the admixing space 3, are two bodies of revolution 8 and 9, which can be rotated relative to one another, between which an annular intermediate space is left. One body of revolution, with the reference 8, is stationary while the other 9 is rotatable. The walls 11 and 12 of the bodies of revolution 8 and 9 respectively have projections 13 and 13 towards the intermediate space 10. The projections 13 of one body of revolution 9 and the projections 13 of the other body of revolution 8 overlap one another in the direction perpendicular to the walls 11 and 12, thus producing a zig-zag path through the intermediate space 10 for the mixture.

The intermediate space 10 lies substantially in the plane of the annular admixing space 3.

The feeding device for the admixture, with pipes 5 and 6 for the individual components of the admixture, is located in the middle of the moulding sand mixer and opens out into the middle of the annular admixing space 3. For mixing the two components together and accelerating them a compressed air line 60 is provided which conducts the compressed air close to the opening outlets of the pipes 5 and 6 for the admixture components. The compressed air line 60 opens out outside the outlet openings of the pipes 5 and 6.

It might be conceivable, in another form of construction, for the compressed air line to conduct the compressed air into the pipe for the admixture material in the vicinity of its outlet opening. It might also be conceivable that the introduction of the admixture material was carried out in the radial direction from the exterior into the admixing space 3.

The outlet opening of the compressed air line is provided with a nozzle 62. The compressed air line 60 is connected to a source of compressed air not shown and provided with a shut -off valve 61. This valve 61 can be operated by remote control.

Disposed on the feeding device is a ring chamber 63 which is open into the admixing space 3 and into which the pipes 5 and 6 for the components of the admixture and the compressed air line 60 open out. The nozzle 62 is inserted in the cylindrical wall of the ring chamber 63 in such a way that the compressed air flows tangentially into the ring chamber 63. The outlet openings of the pipes 5 and 6 for the components of the admixture are directed against the cylindrical wall of the ring chamber 63.

The air vortex produced in the ring chamber 63 thoroughly mixes the components of the admixture and this mixture flows very energetically into the admixing space 3 where the sand is completely saturated with the mixture of air and admixture material.

In this form of construction the two bodies of revolution 8 and 9 are essentially two discs lying parallel to one another. The bodies of revolution might also be in the form of cones, for example.

The projections 13 and 13' are solid annular walls and on the side on which the mixture flows in, i.e. pointing towards the admixing space 3, each has a surface 14 and 14' ascending from 12 and 11, respectively, in the direction of throughflow of the mixture. Between the projections 13 of the body of revolution 9 and the wall 11 of the body of revolution 8 and between the projections 13' of the body of revolution 8 and the wall 12 of the body of revolution 9, a clearance such as that marked is left open in the direction perpendicular to the wall 11 and 12 and is always just sufficient for the passage of. the mixture.

The intermixing of the mixture in the intermediate space is effected by acceleration at the rotating body of revolution 9, slinging along the ascending wall 14, retardation at the projection 13 of the body of revolution 8, slipping on to the body of revolution 9 from the wall 14' and so on.

For the purpose of operating with the foundry mixing machine over a moulding bay in a foundry, the mixing machine is provided with the means of mobile suspension, with eyes 16 for example. This mobile suspension makes it possible to bring the mixing machine into the particular position which is required without any trouble so that the moulding sand mixture can be brought to all points of a flask directly from the mixing machine.

To provide for the possibility of th risk that the sticky mixture might remain adhering to the projections 13' or the walls 14' of the body of revolution 8, the rotating body of revolution 9 is provided with blades, shown at 17. Each blade 17 is fixed at the back of the projection 13 in the direction of through flow of the mixture, extends nearly to the next projection 13 of the other body of revolution 8, and is intended for scraping off any mixture which may be adhering to this projection 13'.

The annular slot 2 is bounded inwardly in the radial direction by .a bell-shaped screen 18 of the feeding device. Inserted in the wall which forms the external boundary of the slot 2 is a valve part 19. The valve part 19 can be slid axially to the bell-shaped screen 18 as far as a saddle surface 21 on the screen. The sliding of the valve part 19 is effected by means of screws 20, for example.

The body of revolution 9 can be rotated by means of an electric motor 22. The electric motor runs at approximately 1300 r.p.m. so that there is no risk as regards spontaneous combustion or explosion of the admixture material.

The electric motor 22 is suspended on a carrier 23 which is connected with the non-rotating body of revolution 8 by way of a pin 24 and a wall 25. The wall 25 and a funnel-shaped part 28 serve to conduct the mixture from the intermediate space 10 to the outlet 7.

The inlet 1 for the sand is provided with a flexible pipe part 26 and a slide valve 27 and is connected to a sandstock bin, which is not shown.

As is shown in FIG. 2, should the foundry mixing machine break down owing to clogging of the intermediate space 10 situated between two bodies of revolution 8, 9, it can be made fit for service again with the utmost speed and simplicity. To this end the bodies of revolution 8 and 9 are held by magnetic force on to the elements 8 and 9 which carry them respectively; and the foundry mixing machine can be opened quickly and easily thus rendering the intermediate space 10 with the bodies of revolution 8 and 9 readily accessible.

The bodies of revolution 8 and 9 are constructed essentially of a non-magnetic material and the elements 8 and 9 which carry the bodies of revolution 8 and 9 of magnetic material. Rigidly built into the bodies of revolution are permanent magnets 8 and 9 respectively, the magnetic force of which holds the bodies of revolution to the supporting elements. The connection is secured from twisting by means of a pin 8 or a flute 9 A housing wall 25 bounding the intermediate space 10 radially outwards is divided axially in the plane of the intermediate space 10 into a part 25 and a part 25 The first part 25 is connected to a part of the foundry mixing machine which has the first body of revolution 8, and the second part 25 is connected with a second part of the foundry mixing machine having the other body of revolution 9. These two parts of the mixing machine are capable of being folded relative to one another by means of a hinge 31. The folding of the two parts together and apart round the axis of the hinge 31 of the mixing machine is effected by means of a servo arrangement which has the reference 32.

In the event of clogging of the intermediate space 10, i.e. if the mixture has adhered firmly to the bodies of revolution 8 and 9, the intermediate space is opened by swinging the two parts of the foundry mixing machine open and removing the bodies of revolution 8 and 9, which are preferably constructed from a light synthetic material, from the elements 8 and 9 which carry them and cleaning them or replacing them by spare parts from stock, after which the two parts of the mixing machine are swung back again and the machine is ready for use again, all this being achieved without any diffuclt dismantling operations.

As is shown in FIG. 3 a foundry mixing machine may also be constructed so as to be divisible in three parts. That is to say a first part, which is essentially an inlet 1 for the sand, a second part, which is the first body of revolution 8 following the inlet 1, and a third part which is essentially an outlet 28 for the sand and which also has the second body of revolution 9 and its driving motor. These three parts of the mixing machine are held together by means of a clamping arrangement 33, 34, 35. The clamping arrangement has a first yoke 33 which is connected to a first mixing machine part, viz the inlet 1, and a second yoke 35 which is connected to the third part of the mixing machine, viz the outlet 28.

The connection between the two yokes 33, 35 is established by means of bars 34. The bars 34 are connected rigidly to the second yoke 35 and guided slidingly in the first yoke 33. Each of the bars 34 is connected to the piston of a servomotor 34 mounted on the first yoke 33, whereby they can be moved in their axial direction.

In the event of the above-described operational breakdown the second yoke 35 can be moved away by means of the servo motors 34, as a result of which the foundry mixing machine opens sufficiently between the inlet 1 and the first body of revolution 8 so that the first body of revolution can be removed from the outlet 28 for the sand. In this example of construction the body of revolution 8 has no magnet. Removal of the first body of revolution 8 renders the other body of revolution 9 freely accessible so that it can be taken away simply by overcoming the magnetic force holding it to the supporting element. The cleaned bodies of revolution 8 and 9 are then replaced in position, the mixing machine is closed by returning the second yoke 35 by means of the servomotors 34 and the unit is then ready for service once again.

It was found that owing to faulty operation there were breakdowns consisting in the fact that after the driving motor had been switched off the sand and the admixture material continued to flow into the intermediate space 10 between the bodies of revolution 8 and 9 and remained there where, as a consequence of the reaction of the admixture material, they developed into a hard and adhesive mass.

As is shown in FIG. 4, the sand and the admixture material are each led through a supply pipe from the stock bin to the admixing space 3 of the foundry mixing machine. The compressed air in the compressed air line 6 60 comes from a compressed air plant which is not shown. The stock bin for the sand is also not shown in the drawing. In the sand supply pipe, which is continuously under pressure from the column of sand in the inlet 1, there is disposed on the annular slot 2 a remotecontrolled pilot valve, of which one of the servomotors is designated by -l9. The admixture material has two components, each of which is conducted from a separate stock bin 36 and 36 respectively by way of a separate supply line to the admixing space 3. For a first component of the admixture there is a stock bin 36 from which the first component of the admixture is supplied by way of a controllable dosing pump 38 which has a driving motor 40 through a supply pipe 5 to the mixing space 3. A pilot valve 5 is disposed on the supply pipe 5. Since the dosing pump runs even when the pilot valve 5 is blocking the supply pipe 5, the pilot valve 5 is in the form of a two-way valve in order to form an overflow arrangement and its first way connects the two parts of the supply pipe 5 connected to the valve 5, while the second is connected to an overflow pipe 39 leading back to the stock bin 36. A remote-controlled servomotor associated with the pilot valve 5 switches in the first or the second valve way.

The portion of the supply pipe 5 between'the pilot valve 5 and the intermediate space 3 is as short as possible and is so constructed that when the pilot valve 5 is in the closed position the admixture material does I not flow out of it.

The pressure in the supply pipe 5 can be regulated by means of the dosing pump 38 through the adjustment of the revolutions of its driving motor 40, for which purpose at least one adjustable potentiometer 41 is" connected before this motor- 40. In this example of construction the regulation of the motor 40, or the dosing pump 38, is carried out by connecting up before the motor 40 three potentiometers 41, 41 41, disposed parallel to one another, each being adjustable to a desired value and capable of being switched into a circuit of the driving motor 40 by means of a selector switch built into a switching device 42. This makes it possible to adjust in advance three desired dosing values which can then be switched on while the foundry mixing machine is in operation simply by operating the selector switch built into the switching device 42, said dosing values being, for example, a value for starting up (high dose position A-B), for normal operation (medium dose position C) and a value before switching off (low dose position D-E). For the second component of the admixture a system is provided which is the same as that already described and which has the stock bin marked 36. The compressed air line 60 is provided with a pilot valve 61.

The pilot valves for the admixture components, one of which is marked 5, the pilot valve 19 for the sand with its servomotors 19, the compressed air pilot valve 61, the driving motor 22 for the body of revolution 9 and the motors 40 of the dosing pumps 38 are all controlled by way of a common switching device 42.

The circuits for the individual switching positions of the switching device are arranged as follows:

in the position marked 0 the driving motor 22, the motors 40 of the dosing pump 38 are switched off and the pilot valves 19 and 5 and 61 are closed; in position A:

driving motor 22 and motors 40, by way of potentiometer 41 are switched on, pilot valves 19 and and 61 are closed;

in position B:

the driving motor 22 and the motors 40 have reached their operating speeds, the pilot valves 19, 5 and 61 are opened;

in position C:

the driving motor 22 is running, the pilot valves 19, 5 and 61 are open, the motors 40 are switched on by way of potentiometer 41 in position D:

driving motor 22 is running, pilot valves 19, 5 and 61 are open, motors 40 are switched on by way of potentiometer 41 in position E:

driving motor 22 is running, motors 40 are running (by way of potentiometer 41 pilot valves 19, 5 and 61 are closed.

In the line between the switching device 42 and the pilot valves 19 and 5 and 61 there is provided a contact breaker 37 by means of which the pilot valves 19 and 5 and 61 can be closed additionally at any time.

FIG. 5 shows that the housing 1 of the foundry mixing machine is connected, for swivelling motion, to an arm 45 which arm 45 in turn is mounted, for rotation about its axis, in an upright which has the general reference 46.

The housing 1 of the foundry mixing machine has two pins 43 situated opposite one another which are rotatably mounted in a fork piece 44 of the arm 45. The arm 45 is mounted, for rotation abouts its axis, in a bearing 46 on the upright 46. To swing the foundry mixing machine relative to the arm 45 there is a servomotor 48 which is connected to the arm 45 and to the housing 1 of the mixing machine. For rotating the arm 45 relative to the upright 46 there is a servomotor 49 which is connected to the arm 45 and the upright 46. These two-servomotors 48 and 49 are controlled together by a device 50 with a control stick 50.

With the above-described features it is possible to shake the mixture on to various places in a moulding bay and the position of the foundry mixing machine required for this purpose can be adjusted simply by the operation of a stick 50 by the operating person.

I claim:

1. A foundry mixing machine for preparing a mixture of sand and an additive having at least two liquid components, the machine comprising a. wall means defining a sand inlet chamber, a preliminary mixing chamber located below the inlet chamber, and an annular slot positioned vertically between said chambers and serving to allow sand to descend by gravity, and in the form of an annular curtain, from the inlet chamber to the preliminary mixing chamber,

b. said slot being defined by cooperating walls which are movable relatively to each other to vary the width of the slot;

c. a feeding and spraying device in the preliminary mixing chamber and including a separate duct for each of said liquid components and an additional duct for compressed air,

d. the ducts leading into the preliminary mixing chamber and being so arranged relatively to each other and to said slot that compressed air admixes the liquid components and propels the admixture into said annular curtain of sand which descends through said slot;

e. an annular final mixing chamber having an inlet at its inner margin which communicates with the preliminary mixing chamber at a region radially outward of said descending annular curtain of sand, and an outlet at its outer margin,

f. the final mixing chamber being defined by a gap bounded by two axially spaced, relatively rotatable bodies of revolution, each of which carries projections which extend toward the gap;

g. a drive motor located below, and connected to cause relative rotation of, said bodies of revolution; and

h. additional wall means which surrounds the bodies of revolution and defines a duct which leads mixture existing from the outlet of the final mixing chamber downward to an outlet located below said bodies of revolution.

2. A mixing machine as defined in claim 1 in which each body of revolution has a base wall from which the projections extend; and the projections of the two bodies overlap one another in the direction normal to said base walls.

3. A mixing machine as defined in claim 2 in which said projections are solid annular walls.

4. A mixing machine as defined in claim 3 in which each projection has, on its upstream side, a surface inclined in the direction of flow of mixture through the final mixing chamber.

5. A mixing machine as defined in claim 3 including blades carried by each projection of one of the bodies of revolution which extend in the direction of flow of mixture nearly to the adjacent projection on the other body of revolution.

6. A mixing machine as defined in claim 1 including magnetic means associated with at least one of the bodies of revolution and serving to hold the body to a supporting element.

7. A mixing machine as defined in claim 6 in which said one body of revolution and said supporting element are made of non-magnetic and magnetic materials, respectively; and including permanent magnet.

means built into said one body of revolution.

8. A mixing machine as defined in claim 1 in which the projections of each body of revolution are spaced axially from the other body a distance just sufficient for the passage therebetween of the mixture.

9. A mixing machine as defined in claim 1 in which the preliminary and final mixing chambers lie in a common plane.

10. A mixing machine as defined in claim 1 in which said ducts have outlets so arranged that the compressed air issuing from its duct impinges upon the liquid components issuing from the other ducts.

1 l. A mixing machine as defined in claim 10 in which the outlet of the compressed air duct is located radially outward of the other outlets.

12. A mixing device as defined in claim 10 in which the outlet of the compressed air duct includes a nozzle for the compressed air.

13. A mixing machine as defined in claim 10 in which the feeding and spraying device includes wall means which defines a feed chamber having a cylindrical side and an open lower end which leads into the preliminary mixing chamber; and the outlets of said ducts open into the feed chamber.

14. A mixing machine as defined in claim 13 in which the outlet of the compressed air duct opens tangentially into said feed chamber.

15. A mixing machine as defined in claim 13 in which the outlets of the ducts for the liquid components are arranged to direct said components against the cylin drical side of the feed chamber.

16. A mixing machine as defined in claim 1 in which' 1' said feeding and spraying device is located at the center of the preliminary mixing chamber.

17. A mixing machine as defined in claim 1 including an enclosing casing having two separable sections- 19. A mixing machine as defined in claim 1 including an enclosing casing having three separable sections, there being an upper section which contains said sand inlet chamber, annular slot and feeding and spraying device, an intermediate section which is formed on the inside as one of said bodies of revolution, and a lower section defined by said additional wall means; and clamping means interconnecting the upper and lower casing sections and holding those sections against the intermediate section.

20. A mixing machine as defined in claim 1 including a supply pipe connected to each of said liquid component ducts and provided with a pilot valve; a servomotor connected to effect relative movement between said slot-defining walls and thereby open and close said 7 slot; and switching means connected to control the drive motor, the pilot valves and the servomoor and having at least a first state in which it switches off the drive motor, causes the pilot valves to block flow of liquid to said ducts and causes the servomotor to effect closure of said slot, a second state in which it energizes the drive motor and maintains the pilot valves and the servomotor in their initial positions, and a third state in which it energizes the drive motor, causes the servomo- 10 tor to open the slot and causes the pilot valves to interconnect the ducts and the supply pipes.

21. A mixing machine as defined in claim 20 in which each supply pipe is connected to receive a liquid component from a variable delivery dosing pump; and each supply pipe is provided with an overflow device which carries away the liquid delivered thereto by the associated pump when the pilot valve blocks flow from the pipe to the associated duct.

22. A mixing machine as defined in claim 2 in which each dosing pump is driven by an electric motor connected with a potentiometer which controls its speed, whereby the delivery rates of the pumps are controlled by the settings of the potentiometers.

23. A mixing machine as defined in claim 22 in which each electric motor is provided with a group of parallel connected potentiometers, and with a selector switch which serves selectively to connect the motor in a circuit with any one of the potentiometers of the associated group.

24. A mixing machine as defined in claim 23 in which the selector switches are incorporated in the switching means and are so arranged that each pump motor is shut off in said first state and runs under the control of different potentiometers in said second and third states.

25. A mixing machine as defined in claim 20 including a pipe connected to supply compressed air to said compressed air duct and provided with a pilot valve; and wherein the pilot valve of the compressed air pipe is connected to be opened and closed by the switching means in unison with the other pilot valves.

26. A mixing machine as defined in claim 1 in which all of said elements are incorporated in an assembly which is mounted for pivotal movement on an arm; and said arm is mounted in an upright standard for rotational movement about its longitudinal axis.

27. A mixing machine as defined in claim 26 including a pair of servomotors, one being connected to pivot the assembly relatively to the arm, and the other being connected to rotate the arm in the upright standard; and common control means, including a control stick,

for operating the servomotors. 

1. A 1foundry mixing machine for preparing a mixture of sand and an additive having at least two liquid components, the machine comprising a. wall means defining a sand inlet chamber, a preliminary mixing chamber located below the inlet chamber, and an annular slot positioned vertically between said chambers and serving to allow sand to descend by gravity, and in the form of an annular curtain, from the inlet chamber to the preliminary mixing chamber, b. said slot being defined by cooperating walls which are movable relatively to each other to vary the width of the slot; c. a feeding and spraying device in the preliminary mixing chamber and including a separate duct for each of said liquid components and an additional duct for compressed air, d. the ducts leading into the preliminary mixing chamber and being so arranged relatively to each other and to said slot that compressed air admixes the liquid components and propels the admixture into said annular curtain of sand which descends through said slot; e. an annular final mixing chamber having an inlet at its inner margin which communicates with the preliminary mixing chamber at a region radially outward of said descending annular curtain of sand, and an outlet at its outer margin, f. the final mixing chamber being defined by a gap bounded by two axially spaced, relatively rotatable bodies of revolution, each of which carries projections which extend toward the gap; g. a drive motor located below, and connected to cause relative rotation of, said bodies of revolution; and h. additional wall means which surrounds the bodies of revolution and defines a duct which leads mixture existing from the outlet of the final mixing chamber downward to an outlet located below said bodies of revolution.
 2. A mixing machine as defined in claim 1 in which each body of revolution has a base wall from which the projections extend; and the projections of the two bodies overlap one another in the direction normal to said base walls.
 3. A mixing machine as defined in claim 2 in which said projections are solid annular walls.
 4. A mixing machine as defined in claim 3 in which each projection has, on its upstream side, a surface inclined in the direction of flow of mixture through the final mixing chamber.
 5. A mixing machine as defined in claim 3 including blades carried by each projection of one of the bodies of revolution which extend in the direction of flow of mixture nearly to the adjacent projection on the other body of revolution.
 6. A mixing machine as defined in claim 1 including magnetic means associated with at least one of the bodies of revolution and serving to hold the body to a supporting element.
 7. A mixing machine as defined in claim 6 in which said one body of revolution and said supporting element are made of non-magnetic and magnetic materials, respectively; and including permanent magnet means built into said one body of revolution.
 8. A mixing machine as defined in claim 1 in which the projections of each body of revolution are spaced axially from the other body a distance just sufficient for the passage therebetween of the mixture.
 9. A mixing machine as defined in claim 1 in which the preliminary and final mixing chambers lie in a common plane.
 10. A mixing machine as defined in claim 1 in which said ducts have outlets so arranged that the compressed air issuing from its duct impinges upon the liquid components issuing from the other ducts.
 11. A mixing machine as defined in claim 10 in which the outlet of the compressed air duct is located radially outward of the other outlets.
 12. A mixing device as defined in claim 10 in which the outlet of the compressed air duct includes a nozzle for the compressed air.
 13. A mixing machine as defined in claim 10 in which the feeding and spraying device includes wall means which defines a feed chamber having a cylindrical side and an open lower end which leads into the preliminary mixing chamber; and the outlets of said ducts open into the feed chamber.
 14. A mixing machine as defined in claim 13 in which the outlet of the compressed air duct opens tangentially into said feed chamber.
 15. A mixing machine as defined in claim 13 in which the outlets of the ducts for the liquid components are arranged to direct said components against the cylindrical side of the feed chamber.
 16. A mixing machine as defined in claim 1 in which said feeding and spraying device is located at the center of the preliminary mixing chamber.
 17. A mixing machine as defined in claim 1 including an enclosing casing having two separable sections which can be parted easily to afford free access to at least one of said bodies of revolution.
 18. A mixing machine as defined in claim 17 in which said separable sections join in a plane along which lies the final mixing chamber.
 19. A mixing machine as defined in claim 1 including an enclosing casing having three separable sections, there being an upper section which contains said sand inlet chamber, annular slot and feeding and spraying device, an intermediate section which is formed on the inside as one of said bodies of revolution, and a lower section defined by said additional wall means; and clamping means interconnecting the upper and lower casing sections and holding those sections against the intermediate section.
 20. A mixing machine as defined in claim 1 including a supply pipe connected to each of said liquid component ducts and provided with a pilot valve; a servomotor connected to effect relative movement between said slot-defining walls and thereby open and close said slot; and switching means connected to control the drive motor, the pilot valves and the servomoor and having at least a first state in which it switches off the drive motor, causes the pilot valves to block flow of liquid to said ducts and causes the servomotor to effect closure of said slot, a second state in which it energizes the drive motor and maintains the pilot valves and the servomotor in their initial positions, and a third state in which it energizes the drive motor, causes the servomotor to open the slot and causes the pilot valves to interconnect the ducts and the supply pipes.
 21. A mixing machine as defined in claim 20 in which each supply pipe is connected to receive a liquid component from a variable delivery dosing pump; and each supply pipe is provided with an overflow device which carries away the liquid delivered thereto by the associated pump when the pilot valve blocks flow from the pipe to the associated duct.
 22. A mixing machine as defined in claim 2 in which each dosing pump is driven by an electric motor connected with a potentiometer which controls its speed, whereby the delivery rates of the pumps are controlled by the settings of the potentiometers.
 23. A mixing machine as defined in claim 22 in which each electric motor is provided with a group of parallel connected potentiometers, and with a selector switch which serves selectively to connect the motor in a circuit with any one of the potentiometers of the associated group.
 24. A mixing machine as defined in claim 23 in which the selector switches are incorporated in the switching means and are so arranged that each pump motor is shut off in said first state and runs under the control of different potentiometers in said second and third states.
 25. A mixing machine as defined in claim 20 including a pipe connected to supply compressed air to said compressed air duct and provided with a pilot valve; and wherein the pilot valve of the compressed air pipe is connected to be opened and closed by the switching means in unison with the other pilot valves.
 26. A mixing machine as defined in claim 1 in which all of said elements are incorporated in an assembly which is mounted for pivotal movement on an arm; and said arm is mounted in an upright standard for rotational movement about its longitudinal axis.
 27. A mixing machine as defined in claim 26 including a pair of servomoTors, one being connected to pivot the assembly relatively to the arm, and the other being connected to rotate the arm in the upright standard; and common control means, including a control stick, for operating the servomotors. 